We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when:
A)an electron moves from the n = 1 to n = 2 state in a hydrogen atom
B)an electron is ionized from a hydrogen atom
C)carbon monoxide (CO)gas is excited by stellar radiation
D)the spin of an electron flips and aligns with the spin of a proton in a hydrogen atom
E)an electron combines with a proton to make a hydrogen atom

Question

Quizplus · Accepted Answer

The 21 cm radiation is emitted when the spin of an electron flips and aligns with the spin of a proton in a hydrogen atom. This transition corresponds to a change in energy levels between the hyperfine states of the ground state of hydrogen. This radiation is able to pass through interstellar dust and can be detected with radio telescopes.

We Detect Neutral Gas in the Interstellar Medium by Looking